Add note for WRF ARM build

doc/README.aarch64.md

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+# Installing WRF on aarch64
+
+## Introduction
+The Weather Research and Forecasting (WRF) Model can be used for fine-scale weather simulation and forecasting, which is one of the important application scenarios of high-performance computing (HPC).
+
+For more information about the WRF, visit the official WRF website.
+
+Programming language: C/Fortran
+
+Brief description: mesoscale weather forecasting model
+
+Open-source protocol: public domain
+
+##### Recommended Version
+The recommended version is WRF V4.2.
+
+## Environment Requirements
+
+### Software Requirements
+| Item  | Version  |  Download Address |
+| ------------ | ------------ | ------------ |
+|  OPENMPI  | 4.0.3  | https://download.open-mpi.org/release/open-mpi/v4.0/openmpi-4.0.3.tar.gz  |
+|  HDF5     | 1.10.6 | https://support.hdfgroup.org/ftp/HDF5/releases/hdf5-1.10/hdf5-1.10.6/src/  |
+|  PNETCDF  | 1.12.1 | https://parallel-netcdf.github.io/wiki/Download.html |
+|  NETCDF-C | 4.7.3  | https://github.com/Unidata/netcdf-c/releases/tag/v4.7.3 |
+|  NETCDF-F | 4.5.2  | https://github.com/Unidata/netcdf-fortran/releases/tag/v4.5.2  |
+|  WRF      | 4.2    | https://github.com/wrf-model/WRF/archive/refs/tags/v4.2.tar.gz  |
+
+### OS Requirements
+| Item  | Version  | How to Obtain  |
+| ------------ | ------------ | ------------ |
+|  CentOS | 7.6  |  https://www.centos.org/download/ |
+| Kernel  | 4.14.0-115  |  Included in the OS image. |
+
+## Configuring the Compilation Environment
+
+### Installing dependencies
+
+```shell
+yum install time -y
+yum install curl* -y
+yum install libcurl-devel -y
+yum install wget -y
+yum install csh -y
+yum install zlib* -y
+yum install perl -y
+yum install make -y
+yum install m4 -y
+yum install file -y
+```
+
+### Installing GNU 9.3
+
+```shell
+yum install -y centos-release-scl
+yum install -y devtoolset-9-gcc
+yum install -y devtoolset-9-gcc-c++
+yum install -y devtoolset-9-gcc-gfortran
+yum install -y devtoolset-9-binutils
+scl enable devtoolset-9 bash
+echo "source /opt/rh/devtoolset-9/enable" >> /etc/profile
+```
+
+### Installing Open MPI
+1. Run the following command to install the system dependency package:
+
+```shell
+yum install libxml2* systemd-devel.aarch64 numa* -y
+```
+
+2. Run the following commands to install Open MPI:
+
+```shell
+wget https://download.open-mpi.org/release/open-mpi/v4.0/openmpi-4.0.3.tar.gz
+tar -zxvf openmpi-4.0.3.tar.gz
+cd openmpi-4.0.3
+./configure --prefix=/path/to/OPENMPI --enable-pretty-print-stacktrace --enable-orterun-prefix-by-default  --with-cma --enable-mpi1-compatibility --enable-mpi-fortran=yes
+make -j $(nproc) all
+make install
+```
+
+3. Configure environment variables:
+
+```shell
+export PATH=/path/to/OPENMPI/bin:$PATH
+export LD_LIBRARY_PATH=/path/to/OPENMPI/lib:$LD_LIBRARY_PATH
+```
+
+### Installing HDF5
+1. Run the following commands to install HDF5:
+
+```shell
+wget https://support.hdfgroup.org/ftp/HDF5/releases/hdf5-1.10/hdf5-1.10.6/src/hdf5-1.10.6.tar.gz
+tar -zxvf hdf5-1.10.6.tar.gz
+cd hdf5-1.10.6
+mkdir -p /path/to/HDF5
+./configure --prefix=/path/to/HDF5 --build=aarch64-unknown-linux-gnu --enable-fortran --enable-static=yes --enable-parallel --enable-shared CC=mpicc CXX=mpicxx FC=mpifort F77=mpifort
+make -j $(nproc)
+make install
+```
+
+2. Configure environment variables:
+
+```shell
+export PATH=/path/to/HDF5/bin:$PATH
+export LD_LIBRARY_PATH=/path/to/HDF5/lib:$LD_LIBRARY_PATH
+```
+
+### Installing PNETCDF
+1. Run the following commands to install PNETCDF:
+
+```shell
+wget https://parallel-netcdf.github.io/Release/pnetcdf-1.12.1.tar.gz
+tar -zxvf pnetcdf-1.12.1.tar.gz
+cd pnetcdf-1.12.1
+mkdir -p /path/to/PNETCDF
+
+./configure --prefix=/path/to/PNETCDF --build=aarch64-unknown-linux-gnu CFLAGS="-fPIC -DPIC" CXXFLAGS="-fPIC -DPIC" FCFLAGS="-fPIC" FFLAGS="-fPIC" CC=mpicc CXX=mpicxx FC=mpifort F77=mpifort
+make -j $(nproc)
+make install
+```
+
+2. Configure environment variables:
+
+```shell
+export PATH=/path/to/PNETCDF/bin:$PATH
+export LD_LIBRARY_PATH=/path/to/PNETCDF/lib:$LD_LIBRARY_PATH
+```
+
+### Installing NETCDF-C
+1. Run the following commands to install NETCDF-C:
+
+```shell
+wget -O netcdf-c-4.7.3.tar.gz https://github.com/Unidata/netcdf-c/archive/refs/tags/v4.7.3.tar.gz
+tar -zxvf netcdf-c-4.7.3.tar.gz
+cd netcdf-c-4.7.3
+mkdir -p /path/to/NETCDF
+./configure --prefix=/path/to/NETCDF --build=aarch64-unknown-linux-gnu --enable-shared --enable-netcdf-4 --enable-dap --with-pic --disable-doxygen --enable-static --enable-pnetcdf --enable-largefile CC=mpicc CXX=mpicxx FC=mpifort F77=mpifort CPPFLAGS="-I/path/to/HDF5/include -I/path/to/PNETCDF/include" LDFLAGS="-L/path/to/HDF5/lib -L/path/to/PNETCDF/lib -Wl,-rpath=/path/to/HDF5/lib -Wl,-rpath=/path/to/PNETCDF/lib" CFLAGS="-L/path/to/HDF5/lib -L/path/to/PNETCDF/lib -I/path/to/HDF5/include -I/path/to/PNETCDF/include"
+make -j $(nproc)
+make install
+```
+
+2. Configure environment variables:
+
+```shell
+export PATH=/path/to/NETCDF/bin:$PATH
+export LD_LIBRARY_PATH=/path/to/NETCDF/lib:$LD_LIBRARY_PATH
+```
+
+### Installing NETCDF-FORTRAN
+1. Run the following commands to install NETCDF-FORTRAN:
+
+```shell
+wget -O netcdf-fortran-4.5.2.tar.gz https://github.com/Unidata/netcdf-fortran/archive/refs/tags/v4.5.2.tar.gz
+tar -zxvf netcdf-fortran-4.5.2.tar.gz
+cd netcdf-fortran-4.5.2
+./configure --prefix=/path/to/NETCDF --build=aarch64-unknown-linux-gnu --enable-shared --with-pic --disable-doxygen --enable-largefile --enable-static CC=mpicc CXX=mpicxx FC=mpifort F77=mpifort CPPFLAGS="-I/path/to/HDF5/include -I/path/to/NETCDF/include" LDFLAGS="-L/path/to/HDF5/lib -L/path/to/NETCDF/lib -Wl,-rpath=/path/to/HDF5/lib -Wl,-rpath=/path/to/NETCDF/lib" CFLAGS="-L/path/to/HDF5/lib -L/path/to/NETCDF/lib -I/path/to/HDF5/include -I/path/to/NETCDF/include" CXXFLAGS="-L/path/to/HDF5/lib -L/path/to/NETCDF/lib -I/path/to/HDF5/include -I/path/to/NETCDF/include" FCFLAGS="-L/path/to/HDF5/lib -L/path/to/NETCDF/lib -I/path/to/HDF5/include -I/path/to/NETCDF/include"
+make -j $(nproc)
+make install
+```
+
+## Compiling and Installing WRF
+1. Run the following command to obtain the source code package:
+
+```shell
+wget -O wrf-v4.2.tar.gz https://github.com/wrf-model/WRF/archive/refs/tags/v4.2.tar.gz
+```
+
+2. Decompress the WRF installation package:
+
+```shell
+tar -zxvf wrf-v4.2.tar.gz
+```
+
+3. Run the following command to switch to WRF source code directory:
+
+```shell
+cd WRF-4.2
+```
+
+4. Run the following commands to configure the pre-compilation environment:
+
+```shell
+export WRFIO_NCD_LARGE_FILE_SUPPORT=1
+export NETCDF=/path/to/NETCDF
+export HDF5=/path/to/HDF5
+export PNETCDF=/path/to/PNETCDF
+export CPPFLAGS="-I$HDF5/include -I$PNETCDF/include -I$NETCDF/include"
+export LDFLAGS="-L$HDF5/lib -L$PNETCDF/lib -L$NETCDF/lib -lnetcdf -lnetcdff -lpnetcdf -lhdf5_hl -lhdf5 -lz"
+```
+
+5. Edit the arch/configure.defaults file and add the following information before line 1977:
+
+
+        ############################################################
+        #ARCH   Linux   aarch64,gnu OpenMPI #serial smpar dmpar dm+sm
+        #
+        DESCRIPTION     =       GNU ($SFC/$SCC)
+        DMPARALLEL      =        1
+        OMPCPP          =        -D_OPENMP
+        OMP             =        -fopenmp
+        OMPCC           =        -fopenmp
+        SFC             =       gfortran
+        SCC             =       gcc
+        CCOMP           =       gcc
+        DM_FC           =       mpif90 -f90=$(SFC)
+        DM_CC           =       mpicc -cc=$(SCC) -DMPI2_SUPPORT
+        FC              =       CONFIGURE_FC
+        CC              =       CONFIGURE_CC
+        LD              =       $(FC)
+        RWORDSIZE       =       CONFIGURE_RWORDSIZE
+        PROMOTION       =       #-fdefault-real-8
+        ARCH_LOCAL      =       -DNONSTANDARD_SYSTEM_SUBR  -DWRF_USE_CLM
+        CFLAGS_LOCAL    =       -w -O3 -c -march=armv8.2-a
+        LDFLAGS_LOCAL   =
+        CPLUSPLUSLIB    =
+        ESMF_LDFLAG     =      $(CPLUSPLUSLIB)
+        FCOPTIM         =       -O3 -ftree-vectorize -funroll-loops -march=armv8.2-a
+        FCREDUCEDOPT    =       $(FCOPTIM)
+        FCNOOPT         =       -O0
+        FCDEBUG         =       # -g $(FCNOOPT)  # -fbacktrace -ggdb-fcheck=bounds,do,mem,pointer -ffpe-trap=invalid,zero,overflow
+        FORMAT_FIXED    =       -ffixed-form
+        FORMAT_FREE     =       -ffree-form -ffree-line-length-none
+        FCSUFFIX        =
+        BYTESWAPIO      =       -fconvert=big-endian -frecord-marker=4
+        FCBASEOPTS_NO_G =       -w $(FORMAT_FREE) $(BYTESWAPIO)
+        FCBASEOPTS      =       $(FCBASEOPTS_NO_G) $(FCDEBUG)
+        MODULE_SRCH_FLAG =
+        TRADFLAG        =      -traditional
+        CPP             =      /lib/cpp -P
+        AR              =      ar
+        ARFLAGS         =      ru
+        M4              =      m4 -G
+        RANLIB          =      ranlib
+        RLFLAGS         =
+        CC_TOOLS        =      $(SCC)
+
+6. Run the following command to generate a configuration file:
+
+```shell
+./configure
+```
+
+When asked for the Linux aarch64 options select `4` (dm+sm).
+When asked whether to compile for nesting select `1` (basic).
+
+7. Run the following command to perform compilation and installation:
+
+```shell
+./compile em_real 2>&1 | tee -a compile.log
+```
+
+8. Check whether the installation is successful:
+
+```shell
+ls main
+```
+
+If wrf.exe file is generated then the installation is successful!